1. Field of the Invention
The present invention relates to a brushless motor and a cooling fan. More specifically, the present invention relates to a layout of a position sensor such as a Hall device or a Hall IC that is used for sensing a magnetic pole position of a rotor in the brushless motor.
2. Description of Related Art
In accordance with a small size and a slim shape of recent electronic equipment, a cooling fan to be used for the equipment is also required to have a small size and a slim shape. In particular, a slim fan having a thickness in the axial direction of 15 millimeters or smaller has little margin in the axial dimension, so it is difficult to secure a space between an end surface of the stator core and the Hall device or the Hall IC. Since the Hall device or the Hall IC senses a magnetic field (or a magnetic flux) generated by a rotor magnet, it is preferable that a distance between the rotor magnet and the Hall device or the Hall IC be small. However, if a distance between the stator core and the Hall device or the Hall IC becomes small, the magnetic field generated by the rotor magnet becomes difficult to sense. A reason for this is considered that the magnetic flux generated by the rotor magnet is attracted strongly to the stator core side so that (leakage) magnetic flux to the Hall device or the Hall IC is weakened.
In particular, if the current that is supplied to a stator coil increases along with an increase in a rotation speed of an impeller of the cooling fan, the magnetic field generated by the rotor magnet is further attracted strongly toward the stator core side. As a result, the Hall device or the Hall IC may not capable of sensing the magnetic field from the rotor magnet correctly. Consequently, the rotation of the impeller may be stopped.